Ammonium dinitramide (ADN) is a solid oxidiser, mainly intended for high performance composite rocket propellants. ADN and other similar compounds are the subject of several patents for application as solid composite rocket propellants and as explosives, both for pyrotechnic applications in general and for other uses, such as in inflators for air-bags.
U.S. Pat. No. 6,113,712 describes stabilisers of ADN. The stabilisers increase the thermal stability and the shelf or service life of the ammonium dinitramide and increase the reliability of the formulations incorporating ADN over extended periods of time and/or after exposure to temperature changes. The use of hexamethylenetetramine (hexamine) to stabilise ADN, under certain conditions, is said to lead to instability and degraded performance and/or safety characteristics in the formulation, either in storage or use. The specification does not mention stabilisation of liquid solutions of ADN.
Published international patent application WO-0050363 discloses a new type liquid monopropellant, which is low-hazardous both from a handling point of view and from an environmental point of view, and does not develop smoke. Such propellant should exhibit the following properties; low toxicity, low flamability, higher theoretical specific impulse (as compared to hydrazine), higher density (as compared to hydrazine), easily ignitable, by means of a controlled ignition mechanism, storable at a temperature between −10 and +70° C., preferably +10 and +50° C., and low sensitivity. Examples of compositions containing ammonium dinitramide, fuel and water are given and shown to have a high specific impulse.
According to the above publication it is also possible to include additives in the propellant. As an example the publication generally states that, since ADN is not stable in acidic environment, small amounts of a suitable base might be added in order to stabilise the dinitramide.
For the purpose of orbit maneuvering and attitude control of satellites and other space vehicles, rocket engines are often used in short bursts or pulses, the duration of which typically can be fractions of seconds to several minutes. For such purposes small rockets are commonly used with a thrust of, for example, 1 to 50 N. Especially in such applications it is important that the combustion in the engine is stable, i.e., for example, does not exhibit fluctuating pressure characteristics in the reaction chamber. Stabile combustion conditions should preferably be established instantaneously after ignition of the propellant, or at least combustion conditions should only change slowly in a predictable way, so as to readily be able to be compensated for.
Accordingly, it would be desirable to have a suitable propellant for such purposes available, which propellant also should exhibit the above-mentioned desired characteristics of the above-mentioned liquid monopropellant.
According to the present invention this task is solved by providing a propellant of the preamble of claim 1, exhibiting the features of the characterising portion of claim 1.